SAN MARCOS, Calif. - A threatening but unsubstantiated social media post about a potential school shooting at San Marcos High School has sparked an investigation and will have sheriff's deputies on high alert Tuesday at the high school and other San Marcos campuses, school district officials said.

"This evening we were alerted to social media rumors of a possible shooting at San Marcos High School," San Marcos Unified School District Superintendent Melissa Hunt said in a message posted to social media and sent to parents in an email Monday night. "Law enforcement is actively investigating. Deputies will be posted at the school tomorrow. While these rumors are unsubstantiated at this point we are taking them seriously."

Detectives determined the image being spread through social media was related to a recent arrest in South Carolina regarding a school shooting threat, according to San Diego County Sheriff's Sgt. Daniel Deese.

"With cooperation from the social media outlet, it appears there were no specific threats targeting San Marcos High School, but images from the South Carolina incident were reposted," Deese stated.

Hunt also thanked the community members who informed the district of the threat and assured parents that "your students will be safe and protected at school."

"There will be increased law enforcement presence around our schools and community," Hunt said. "The district is in constant communication with law enforcement and will be sharing information as we receive it."

The reassurances that students would be safe were not enough for many parents.

"Keeping our son home from San Elijo (Middle School)," wrote parent Heather Fusting on Facebook. "Not worth the chance."

On Twitter, Fusting tweeted at the district that "lots of us parents choosing to keep kids home not only from high school but surrounding schools as well."

Dozens of other parents responded to the district's Facebook post saying they were contemplating or had already decided to keep their children home from school. Many also worried that the specific threat to the high school would be used as a distraction for an attack on a different area school.

"Thank you, reading all of you reassures my conviction of keeping my child home tomorrow!" wrote parent Adreanna Vivi Bejarano.

Earlier this school year, a student at Poway High School texted friends that "there would be a shooting at the school" and posted an image of the conversation on social media, though authorities investigated the claim and ultimately said the threat was unfounded.

Roughly two weeks after that threat, near the end of October of last year, students at Meadowbrook Middle School in Poway were found on consecutive days to be carrying "hit lists" containing the names of classmates and faculty at the school.